WAVE CHARACTERISTICS IN THE TROPOSPHERE AND STRATOSPHERE OVER THE INDIAN TROPICS DURING THE DYANA PERIOD

One of the important scientific objectives of the international DYANA campaign was to obtain the characteristics of planetary scale waves in the low-latitude middle atmosphere. India participated in this campai gn by way of launching several rockets and high-altitude balloons from a number of locations to determine the vertical structure of differen t wave modes present during January-March 1990. Rocket launchings were conducted from two stations, namely Thumba (8.5-degrees-N, 77.0-degre es-E) with M-100 rockets and Balasore (21.5-degrees-N, 87.0-degrees-E) with RH-200 rockets, while balloons were launched from three stations , i.e. Trivandrum near Thumba, Minicoy (8.2-degrees-N, 73.0-degrees-E) and Port Blair (11.7-degrees-N. 92.7-degrees-E). In addition. there w ere balloon flights from Hyderabad (17.3-degrees-N, 78.3-degrees-E) an d Bhubaneshwar (20.2-degrees-N, 85.5-degrees-E). The results of the sy noptic scale wave activity as obtained from various data sources are g iven here. Three prominent peaks with wave periods near 6 8 days (shor t periods), 10-12 days (medium periods) and 30-45 days (long periods) are found to occur at all the stations, The medium- and long-period wa ves appear to be forced Rossby modes penetrating from midlatitudes whi le short period waves all have characteristics matching those of mixed Rossby-gravity waves. A very interesting result is the presence of lo ng-period oscillations in the upper stratosphere and mesosphere, with very large amplitude, contrary to earlier observations.